The Flow Cytometry Shared Resource provides AECC investigators with convenient and affordable access to a broad spectrum of important technologies in flow cytometry, and supports numerous research studies that rely on high speed fluorescence activated cell sorting (FACS) and advanced multiparameter fluorescence analysis. In addition to providing advanced flow cytometry equipment, the shared resource provides technical expertise and training to guide AECC investigators and their staff in the application of basic and advanced flow cytometry techniques. The facility also organizes and supports a program of seminars on new technologies that inform AECC investigators about newly emerging applications of FACS that can enhance their research. The major usage of this shared resource is for multiparameter analysis and high speed sorting of cell populations based on labeling with fluorochrome-conjugated antibodies or other fluorescent protein or chemical dye reagents. Training of many investigators in the use of the facility's analytical instruments has led to a very large and well-trained user base. During 2005-2006, the facility provided services to more than 275 registered users, consisting of faculty, postdoctoral fellows, students and technicians from 78 different laboratories. AECC members were principal investigators of 45 of these laboratories, and two thirds of total hours of usage of all facility services in 2005-2006 was attributable to the laboratories of AECC investigators. These investigators have access around the clock and seven days per week to the facility's analyzers, which include Becton-Dickinson FACScan (one laser, 3-color), FACSCalibur (two laser, 4-color), and LSR-II (4 laser, 12 color) instruments. Standard fluorescent microscopes and computer work stations with an extensive software library for processing of FACS data are also routinely available. High speed cell sorting with the facility's 3-laser, 8-color Dako-Cytomation MoFlo sorter is performed exclusively by the trained facility staff during regularly scheduled weekday hours. This shared resource has numerous value-added features, and receives substantial institutional support that has greatly assisted the acquisition of state-of-the-art instrumentation and a superb staff of flow cytometry experts.